Production of x-rays

Question 1

function of the collimator

Answer 1

narrows the beam of x-ray

Question 2

if the incident elecectron hits the nucleus what happens?

Answer 2

• highest energy given off as an x-ray
• energy given off is equivalent to the energy coming in
• called a bremsstrahlung x-ray

Question 3

what happens when the incidence electron comes close to but does not hit the nucleus?

Answer 3

• the negatively charged electron is attracted to the + nucleus but this does not hit the nucleus.
• the direction is changed and it looses energy.
• moderate to medium x-ray given off

Question 4

when the incident electron comes further away from the nucleus what happens in bremsstrahlung x-rays?

Answer 4

• energy is lost from deceleration and it bend less than if closer.
• a low energy x-ray is given off

Question 5

bremsstrahlung x-rays high energy radiation?

Answer 5

High Energy -electrons directly collide with a nucleus, producing a high energy photon (in keV) that is equal in energy to the incident electron.

Question 6

bremsstrahlung x-rays medium energy radiation

Answer 6

Medium Energy – Produced by electrons passing close to the nucleus causing deflection and deceleration of the electron. This deceleration causes the electron to lose some of its energy in the form of photon radiation.

Question 7

bremsstrahlung x-rays low energy radiation

Answer 7

Low Energy – Produced when electrons pass at a distance from the nucleus. They are deflected and slowed somewhat, producing a low energy photon.

Question 8

how are x-rays produced in characteristic radiation?

Answer 8

• the incident electron hits an electron in orbit and it kicks the electron out of the orbit
• the hole in the inner ring is not favorable and an electron from the next electron shell jumps down to fill the gas. - cascade effect starts causing energy to be given off in photons

Question 9

cathode of x-ray tube is positive or negative?

Answer 9

negative

Question 10

anode of x-ray tube is positive or negative?

Answer 10

positive

Question 11

why is tungston used as the target in the x-ray tube?

Answer 11

Has to have a high atomic number, high melting point, high thermal conductivity and low vapor pressure. Tungsten meets all of these requirements.

Question 12

what is the focal spot?

Answer 12

That point on the target where the stream of x-ray photons originates. Should be as small as possible for the best radiographs yet must be large enough to dissipate heat. Placing target at an angle provides a smaller effective focal spot for sharp images while maintaining a larger actual focal spot for heat dissipation.
-the kinetic energy of electrons produced from the cathode are focused by the molybendeum cup on the focal spot and here they are converted to x rays (at the anode)

Question 13

A molybdenum focusing cup in an x-ray tube
A. narrows the beam of electrons
B. is located in the cathode
C. directs electrons toward the tungsten target
D. all of the above

Answer 13

D- All the above

Question 14

function of the cathode?

Answer 14

-Cathode (-) : A tungsten filament and molybdenum focusing cup provide the source and direction of electrons of the cathode ray. Low voltage is applied to heat the filament, producing a cloud of electrons through thermionic emission. The molybdenum focusing cup electrostatically focuses the electrons into a narrow beam.

FYI the current goes from the cathode to the anode.

Question 15

function of the anode?

Answer 15

-Anode (+): The tungsten target and copper stem convert the kinetic energy of the electron stream of photons to x-rays and heat.

Question 16

If you wish to increase the energy of the emitted x-ray beam, you would:

A. increase power to the high voltage step up transformer
B. increase power to the low voltage tube current
C. increase the size of the focal spot
D. all of the above

Answer 16

A. increase power to the high voltage step up transformer

Question 17

doubling the time does what?

Answer 17

doubles the exposure

Question 18

the quantity of radiation produces is ________ to the tube current?

Answer 18

directly proportional

Question 19

as tube current (mA) is increased what happens?

Answer 19

more electrons are released to collide with the target

-more collisions = more radiation

Question 20

increasing mA vs increasing KeV?

Answer 20

• increase mA = increase the number of electrons produced at the filament
• higher KVP= fater the electrons accelerate to the target

Question 21

what part of x-rays wears out fastest?

Answer 21

-tungston filament burnout = xray machine should be left on. strain on filament when warmed and cooled

Question 22

increasing the potential between the anode and cathode _____ the energy of each electron when it strikes the target?

Answer 22

increases

Question 23

_____ KVP _______ x-rap penetration?

Answer 23

increase KVP increases x-ray penetration

Question 24

filtration absorbs what?

Answer 24

aluminum filter lowers the energy photons to eliminate them so not absorbed by the body.

Question 25

function of the collimation?

Answer 25

• reduce the size of the x-ray beam
• reduces scatter radiation and patient surface exposed
• lined with lead

Question 26

source to object distance inverse square law

Answer 26

intensity of x-ray beam is inversely proportional to the square of the distance between the source and the target.

Question 27

what happens to the number of photons or energy reaching the target when the distance is doubled?

Answer 27

energy cut in 1/4

Question 28

what happens to the number of photons or energy reaching the target when the distance is tripled?

Answer 28

energy is 1/9

Question 29

You expose an x-ray and it comes out underexposed. How do you try to correct the exposure on a retake?

A.move tubehead back to increase focal distance
B. increase kVp on the control panel
C. increase exposure area by using a round collimator
D. increase exposure time

Answer 29

B. increase kVp on the control panel - prefered answer
also
D. increase exposure time - to correct expoure

Question 30

when does coherent scattering occur?

what can it cause?

Answer 30

• occurs when low energy photons are deflected by outer ring electrons.
• Accounts for only about 7% of interactions in dental, so contributes very little to film fog on image.

Question 31

what is photoelectric absorption?

what does it look like?

Answer 31

• process in which incident photons are absorbed by an atom by interacting with inner shell electrons.
• This is what makes the lighter areas on the film, making radiographic imaging possible.

Question 32

what does photoelectric absorption depend on?

Answer 32

• density and thickness of the object, thus creates the contrast between different tissues in a film.
• ex metal shows up white, air - black

Question 33

when does compton scattering occur?

Answer 33

• when a photon interact with an outer orbital electron = lower energy x-ray
• scattered photons darken and degrade the image while carrying no useful information
• accounts for about 49% of interactions in dental radiography

Question 34

what type of photons are more readily absorbed as the travel through matter?

Answer 34

lower energy photons

Question 35

what happens as the energy of the photon beam increases in regards to the transmission of the beam?

Answer 35

transmission of the beam through the absorber increases

Question 36

Which of the following photon interactions make it possible to produce radiographic images:

A. coherent scattering
B. photoelectric absorption
C. Compton scattering
D. all of the above

Answer 36

B. photoelectric absorption

Question 37

low voltage tube current

Answer 37

heats the tube filament generating a stream of electrons between the cathode and anode

Question 38

high tube voltage

Answer 38

between the cathode and anode accelerated the electron stream to a level that x-rays can be produced

Question 39

why is the x-ray device in a vacuum tube?

Answer 39

• no gas molecules for electrons to collide with

- no oxidation or burnout of filament

Question 40

the tungston target is located at what end of the x-ray machine?

Answer 40

the positive anode

Question 41

coherent vs compton scattering?

Answer 41

• coherent: -occurs when low energy photons are deflected by outer ring electrons. -Accounts for only about 7%
• compton: -when a photon interact with an outer orbital electron = lower energy x-ray-scattered photons darken and degrade the image while carrying no useful information. accounts for about 49% of interactions in dental radiography